Clarify doc for loading custom extensions
minor doc fix: s/various some/various/
Customizes tabline appearance: type, close button

This commit adds a couple of new settings so that it's possible to hide
the tab type (all the way to the right) and the symbol which represents
the close button.

The settings and their defaults:

let g:airline#extensions#tabline#show_tab_type = 1
let g:airline#extensions#tabline#close_symbol = 'X'
Improve colour highlights

- Sol: Used a less distracting color to show a modified file/buffer
- Sol: Similar change as above, to tabline as well
- Sol: Warning colour imporved (Previously was some bad shade of magenta)
- Sol: All the Above mentioned changes replicated for CTERM values as well
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- Luna: `Inactive Modified` colour is improved (Was a shade of red
                                                that was hard to read)
Merge pull request #464 from emilyst/customize-tabline-close-and-type

Customizes tabline appearance: type, close button
Merge pull request #466 from Pychimp/master

Improvements to Sol and Luna themes
Merge pull request #442 from blueyed/doc

Minor doc fixes
filter() result error
My fault, it's a transferred error, add a '\' that' works fine.
Merge pull request #467 from xinleibird/master

filter() result error
Fixes incorrect fg value in visual modified

- changes it from white (hard to read) to dark grey-ish (easier to read)
Merge pull request #468 from Pychimp/master

Fixes incorrect fg value in visual modified
Save branch head to a buffer variable

Save branch head to a buffer-local variable to prevent looking up the VCS head for every status line refresh.
Add CursorHold autocmd to unset airline_head
Merge pull request #469 from russellhancox/patch-1

Save branch head to a buffer variable
remove usage of fugitive#detect as per request

https://github.com/tpope/vim-fugitive/issues/463
restore original directory change detection. also resolves #474.
Now trailing tabs are also reported, fixed bug when trailings with mixed tabs and spaces were being reported as mixed indents, case when count of spaces at the end of tabbed indentation less then tabstop does not reported as mixed indent anymore.
Merge pull request #478 from davits/mixed_indent

Improvements in whitespace plugin
handle cases where the augroup has not be defined yet. resolves #492